BEIJING, Oct 21 (Reuters) - The economic impact of China's tough campaign against smog this winter is expected to be limited, a senior state planning official said on Saturday.

"Measures to fight pollution don't have a big impact on economic growth," Zhang Yong, vice-chairman of the National Development and Reform Commission, told reporters during a briefing.

As many as 28 cities in northern China have vowed to slash industrial output this winter in a bid to cut smog by at least 15 percent and meet politically important air quality targets for this year. (Reporting by Kevin Yao and Meng Meng; Writing by David Stanway; Editing by Kim Coghill)